Amino acids such as L-lysine, L-glutamic acid, L-threonine, L-leucine, L-isoleucine, L-valine and L-phenylalanine are industrially produced by fermentation by using microorganisms that belong to the genus Brevibacterium, Corynebacterium, Bacillus, Escherichia, Streptomyces, Pseudomonas, Arthrobacter, Serratia, Penicillium, Candida or the like. In order to improve the productivity, strains isolated from nature or artificial mutants thereof have been used as these microorganisms. Various techniques have been disclosed for enhancing activities of L-glutamic acid biosynthetic enzymes by using recombinant DNA techniques, to increase the L-glutamic acid-producing ability.
The productivity of L-amino acids has been considerably increased by breeding of microorganisms such as those mentioned above and the improvement of production methods. However, in order to meet further increase in the demand in future, development of methods for more efficiently producing L-amino acids at lower cost have still been desired.
As methods for producing amino acids by fermentation of methanol which is a fermentation raw material available in a large amount at a low cost, there have conventionally known methods using microorganisms that belong to the genus Achromobacter or Pseudomonas (Japanese Patent Publication (Kokoku) No. 45-25273/1970), Protaminobacter (Japanese Patent Application Laid-open (Kokai) No. 49-125590/1974), Protaminobacter or Methanomonas (Japanese Patent Application Laid-open (Kokai) No. 50-25790/1975), Microcyclus (Japanese Patent Application Laid-open (Kokai) No. 52-18886/1977), Methylobacillus (Japanese Patent Application Laid-open (Kokai) No. 4-91793/1992), Bacillus (Japanese Patent Application Laid-open (Kokai) No. 3-505284/1991) and so forth.
So far, however, no method has been known for producing L-amino acids by using Methylophilus bacteria. Although methods described in EP 0 035 831 A, EP 0 037 273 A and EP 0 066 994 A have been known as methods for transforming Methylophilus bacteria by using recombinant DNA, applying recombinant DNA techniques to improvement of amino acid productivity of Methylophilus bacteria has not been known.